... The name Salm (for τ Pegasi, Kerb) is also the name of the eldest son of king Fereydun, another name of which was Apam Napat ('Son of Waters'):

Salm is a character in the Persian epic Shahnameh. He is the oldest son of [the] legendary hero and king Fereydun. It is believed that his name was given to him by his father, after Salm chooses to seek safety and run instead of fighting the dragon that had attacked him and his brothers (the dragon was Fereydun himself who had disguised himself to test his sons) ...

When Fereydun decides to divide his kingdom among his sons, he gives Salm [the timid unmanly one] Anatolia and West [the female side of the kingdom] ... Fereydūn ... [is] also called Apam Napat, 'Son of the Waters' ...

... τ, 4.5, with ν, was Al Sufi's Sa'd al Na'amah, which Knobel thinks should be Al Na'āim, the Cross-bars over a well; but they also were known as Al Karab, the Bucket-rope. The usual titles for τ - Markab and Sagma or Salma - are from Bayer, but the last two should be Salm, a Leathern Bucket.

Some kind of rope (karab) is needed to draw up a water bucket and we should here add:

"With δ and ζ it [β Piscis Austrinus] was the Chinese Tien Kang, the Heavenly Rope." (Allen)

This rope is not vertical but oriented horizontally, as if it was used to draw something forward in time instead of upwards in space.

In rongorongo times β Piscis Austrinus was rising heliacally in February 25 and the preceding vae glyph is likely to represent a time with exceptionally much (paupau) water, a deluge at the end of the exceptionally long manzil Saad Al Thabib:

Saad Al Thabib 11	12	13	14	15 (285)
February 21	22	23	24	25 (56)
Ca12-21	Ca12-22	Ca12-23 (339)	Ca12-24	Ca12-25
te niu ku hakatu ua	te maitaki - kupega tuku hia mai	mata hakatuu	te vae paupau	te niu tutuu
λ Piscis Austrini (336.8), ε Cephei (337.2), Ancha (337.4)	ρ Aquarii (338.2)	Sadachbia (338.6), π Aquarii (339.5)	ρ Cephei (340.2), ζ Aquarii (340.4), Alrediph (340.5)	σ Aquarii (340.9), Homan, β Piscis Austrini (341.2)
August 23	24 (236)	25	26	27
An Nathra 7	8	9 (101)	10	11
Simiram, Adhafera, Tania Borealis (154.7), Algieba, q Carinae (155.5)	Tania Australis (156.0)	μ Hydrae (157.1)	no star listed	Shir (158.9), p Carinae (159.3)

	Saad Balaa 1	2
	26 (422)	27 (58)
	Ca12-26	Ca12-27
	oho te rima o te niu	a hagahaga
	υ Aquarii (341.9), η Aquarii (342.1)	Situla (342.7), ε Piscis Austrini (343.5)
	August 28 (240)	29
	An Nathra 12	13 (105)
	φ Hydrae (160.3)	no star listed

We should not abandon our table for investigating the lucky (sa'ad) time towards the close of the manzil year:

Nawaa	Manzil	Begins on	Number of days		Stars
Ash Shabt (Sagittarius)	18 Al Naam	16 Jan (381)	13	257	Ascella & Nunki (ζ, ς)
	19 Al Baldaah	29 Jan (394)	13	270	Al Baldah (π)
The Three Saads (< 22h)	20 Saad Al Thabib	11 Febr (407)	15	285	Saad Al Thabih
	21 Saad Balaa	26 Febr (422)	13	298	Albali (ε)
	22 Saad Al Saud	11 March (435)	13	311	Sadalsud (β)
22h					Sadalmelik (α)
Hameemain (> 22h)	23 Saad Al Akhbia	24 March (448)	13	324	Sadachbia (γ)
	24 Almuqaddam	6 April (461)	13	337	Almuqaddam

Looking again in my star list, searching between Al Baldah (π Sagittarii) and Albali (ε Aquarii) for a likely candidate to translate 'Saad Al Thabih' with, the distance is 314.8 - 290.1 = 24.7 days. In the interval from day 295 to day 310 there are these stars:

Albireo	β Cygni	3.05	27° 51′ N	19h 29m	296.5
Sham	α Sagittae	4.39	17° 54′ N	19h 38m	298.8
Tarazed	γ Aquilae	2.72	10° 29′ N	19h 44m	300.3	H
Altair	α Aquilae	0.76	08° 44′ N	19h 48m	301.3	H
	ι Sagittarii	4.12	41° 52′ S	19h 52m	302.2
Terebellum	ω Sagittarii	4.70	26° 18′ S	19h 52m	302.3
Alshain	β Aquilae	3.71	06° 17′ N	19h 53m	302.6	H
	ε Pavonis	3.97	72° 55′ S	19h 56m	303.3
	θ Sagittarii	4.37	35° 17′ S	19h 56m	303.3
	μ Pavonis	5.32	66° 57′ S	19h 57m	303.7

	δ Pavonis	3.55	66° 11′ S	20h 04m	305.4
Shang Wei	κ Cephei	4.38	77° 43′ N	20h 07m	306.2
	ξ Capricorni	5.84	12° 37′ S	20h 10m	306.8
Gredi	α Capricorni	3.58	12° 42′ S	20h 15m	308.2
	σ Capricorni	5.28	19° 07′ S	20h 16m	308.5
Alshat	ν Capricorni	4.77	12° 46′ S	20h 18m	308.9
Dabih	β Capricorni	3.05	14° 47′ S	20h 18m	309.0	C
	κ Sagittarii	5.60	42° 03′ S	20h 19m	309.1
Sadir	γ Cygni	2.23	40° 06′ N	20h 20m	309.4
Peacock	α Pavonis	1.94	56° 53′ S	20h 21m	309.7
Okul	π Capricorni	5.08	18° 13′ S	20h 25m	310.6
Bos	ρ Capricorni	4.77	17° 49′ S	20h 26m	310.9
	ο Capricorni	5.94	18° 35′ S	20h 27m	311.2
	θ Cephei	4.21	63° 00′ N	20h 28m	311.5

If 'Saad Al Thabih' should be in Sagittarius, then the likely candidate could be Terebellum (ω), the quartet of stars at the rump of the horse:

But possibly 'Saad Al Thabih' corresponds to Altair (α Aquilae) in the Hindu station Sravana:

20	Purva Ashadha	δ and ε Sagittarii	Elephant tusk, fan, winnowing basket
21	Uttara Ashadha	ζ and σ Sagittarii	Elephant tusk, small bed
22	Abhijit	α, ε, and ζ Lyrae	-
23	Sravana	α, β, and γ Aquilae	Ear or Three Footprints
24	Dhanishta	α - δ Delphini	Drum or flute
25	Shatabisha	γ Aquarii	Empty circle, 1000 flowers or stars
26	Purva Bhādrapadā	α and β Pegasi	Swords or two front legs of funeral cot, man with two faces
27	Uttara Bhādrapadā	γ Pegasi and α Andromedae	Twins, back legs of funeral cot, snake in the water
28	Revati	ζ Piscium	Fish or a pair of fish, drum

"Shravana ...  is the 22nd nakshatra or lunar mansion as used in Hindu astronomy and astrology. It belongs to the constellation Makara or Capricorn." (Wikipedia)

Evidently there is confusion here. On one hand Wikipedia has given me the triplet of main stars in Aquila (together with 'Three Footprints') as the ruling stars of the station Sravana, on the other hand the station Shravana is said to belong to the Capricorn (Makara). Then Wikipedia warns not to confuse Shravana with Shraavana':

"Śrāvaana is a month of the Hindu calendar. In India's national civil calendar, Śrāvaana is the fifth month of the Hindu year, beginning in late July and ending in the third week of August. In the Tamil calendar, it is known as Āadi and is the fifth month of the solar year. Śrāvaana  begins with the Sun's entry into Leo. In lunar religious calendars, Śrāvaana begins on the new moon and is the fifth month of the year."

When in rongorongo time Sun arrived at the nose of Leo it was August 10:

Al Baldaah 9	10	11 (268)
February 6	7 (403)	8
Ca12-6	Ca12-7	Ca12-8 (324)
tagata hoi haatu	ka huri ra	ki te mauga
φ Capricorni (321.8)	Alderamin (322.9), Dai (323.5)	γ Pavonis (324.1)
August 8 (220)	9	10
Murzim 5 (84)	6	7
Tureis (139.8)	Markab Velorum (141.5)	Al Minhar al Asad (141.6), Alphard (142.3)

The Moon station at that time ought to have been around day 222 (August 10) - 182 = 40, i.e. around February 9:

Al Baldaah 11	12	13 (270)	Saad Al Thabib 1	2
8	9 (40)	10	11	12 (408)
Ca12-8	Ca12-9 (325)	Ca12-10	Ca12-11	Ca12-12
ki te mauga	oho te vae	ki hukiga o te ra	kua oho ra	kua ere te tagata - te hetu
γ Pavonis (324.1)	Yan (324.6)	Alphirk (325.7), Sadalsud (325.9)	Castra (327.2), Bunda (327.5)	Nashira (328.0)
August 10	11	12	13	14 (226)
Murzim 7	8	9	10	11 (90)
Al Minhar al Asad (141.6), Alphard (142.3)	ω Leonis (142.6), τ¹ Hydrae (142.7), ψ Velorum (143.3), Alterf, τ² Hydrae (143.4), ξ Leonis (143.5)	A Hydrae (144.1)	Ukdah (145.4),  κ Hydrae (145.5)	Subra (145.8), ψ Leonis (146.4)

As the manzil Saad Al Thabib was beginning just after the heliacal rising of Sadalsud (already used for the manzil Saad Al Saud) the star 'Saad Al Thabih' can hardly have anything to do with with Shraavana.

I am left with 3 alternatives for explaining 'Saad Al Thabih': Terebellum in Aquarius, Altair in Aquila, or some star in Capricornus, possibly Gredi (α) or Dabih (β):

The Chinese list decides it:

1	Horn	α Virginis	Crocodile
2	Neck	κ Virginis	Dragon
3	Root	α² Librae	Badger
4	Room	π Scorpii	Hare
5	Heart	σ Scorpii	Fox
6	Tail	μ¹ Scorpii	Tiger
7	Winnowing Basket	γ Sagittarii	Leopard
8	South Dipper	φ Sagittarii (?)	Unicorn
9	Ox / Herd Boy	β Capricornii	Buffalo
10	Girl	ε Aquarii	Bat
11	Emptiness	β Aquarii	Rat
12	Rooftop	α Aquarii	Swallow

Dabih (β Capricorni´), at the head of the Goat, is a name closely resembling Thabih:

Nawaa	Manzil	Begins on	Number of days		Stars
Ash Shabt (Sagittarius)	18 Al Naam	16 Jan (381)	13	257	Ascella & Nunki (ζ, ς)
	19 Al Baldaah	29 Jan (394)	13	270	Al Baldah (π)
The Three Saads (< 22h)	20 Saad Al Thabib	11 Febr (407)	15	285	Dabih (β Capricorni)
	21 Saad Balaa	26 Febr (422)	13	298	Albali (ε Aquarius)
	22 Saad Al Saud	11 March (435)	13	311	Sadalsud (β)
22h					Sadalmelik (α)
Hameemain (> 22h)	23 Saad Al Akhbia	24 March (448)	13	324	Sadachbia (γ)
	24 Almuqaddam	6 April (461)	13	337	Almuqaddam