I have one of the fish tank vacuum cylinders from Petco. I never really was happy with the entry end, ended up flairing it under heat, and that made it tolerable.
I just read the other day about Plasti-dip, and just so happens that I have been experimenting with black and white Plastidip to make an oversize ring fit properly.
I used it on the cylinder…I got to tell you, ITS FRIGGIN GREAT!!!!!
I do think the white works better than the black, seems to hold up much better. If you are going to use it, you only have to wait 20-30 minutes to add another coat.
Build up the lip as thick as you want, I found it not only made it super comfortable, it also acts as a cock ring around my shaft base and makes pumping work even better!
After you put on as many coats as you think you need, let it dry overnite to make sure it is totally cured before you use it. It shrinks quit a bit when dry, but you can always add a few more dips if you want to.
Make sure you clean it well with soap and water and dry it before you add any coats after you have used it. If this holds up well to use, I will probably make a thread on it so others can see it easily.
ps I bought a Harbor Freight pump for $16.99 at the store, great solid pump!