You didn't indicate wtc size. If wtc is short you may need a small (3 pack lipo) to accomodate the wtc length. My Kilo (39") uses a 3 pack.

If you are talking about a pump to blow a ballast tank, I use a micro pump from Nautilus Drydocks. Cost about $15usd + shipping.

Good advice! I know Bob Martin very well and have been to his site often. Just trying to find alternative suggestions to how best "seal" WTC end caps.
If you are familiar with wtc's you know for several reasons we need to open an end cap after each submergence. This creates a possible leak source
when resealed.
To prevent leakage I open an end cap only to make internal repairs. I charge the battery and remove any accumulated wtc moisture without disturbing end cap seals.
Took some doing, and with a great amount of help from a fellow Submarine builder but the system works very well.
If any one reading this wants some detail, I will be glad to answer questions.

Did you try a youtube search?: revell 1/72 gato rc build

The Nautilus Drydock is a super cool site. Looks like they have a great build/info kit for just 40 bucks!

I think you may be able to find that information here: https://www.rc-submarine.com/.
If not, try at The SubCommittee.com