My situation was I have a large combined waste tank (200 gal.) and a 140 fresh tank. The senders I used drop down from inside the coach so I put a small access plug that I can get to if I ever need to change or replace them. One of the problems I had with my old sender for the waste tank was junk (use your imagination) on the sender. The salesman and Wema suggested using a gauge that starts a ½ tank which works really great. The heavy ends are at the bottom and do not hang up on the sender. I have been using it for 3 years now without problems. The fresh tank works great and is very accurate.
There are other senders that stick into the tank that don't have a float like the Wema has. Snake River Electronics is one, but their senders probably only work with their tanks.