Pictures would be very helpful
Where did you get this tank?
Grey tank
S/B two 1.5" openings on top
One for Roof Vent line
One for sink drain line (which should also have an Air Admittance Valve just after sink 'P' trap
S/B one 1.5" opening either on bottom (not common) or sidewall near bottom for dump line
**Bottom drain not common due to limitations in location in RVs. Bottom drain would require tank to slope all 4 ways to bottom drain plus dump line then sticks down enough for elbow/slope to drain line which could cause it to hang way down.
Easier to side drain.....slope tank towards drain hole and then dump line doesn't hang so low
Sounds like you have a fresh water tank.
Fill opening, vent opening, cold water line supply, overflow opening, drain opening etc
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31