Pumpout may be possible, but probably a pain in the ass to do. First thing to do would be to see if you have room inside for a pump out. Being that I do not see a sniper model that offers a pumpout, I would guess there would not be enough room for it inside. You would also have to put another hole in your fill tank and body, and rout everything properly, and cut out for another switch. Too much work and you may fook up your machine.
Remember, for most smaller residential jobs, a 5 gallon Homer bucket is a Porty Hacks best friend.
A twelve foot sink lead with an on/off valve at the end that can be fed into your fill tank and safely controlled may be a better option for auto-filling, although not as glamorous.
I feel auto-filling inside on a average residential job is more work than benefit, and can be a liability.
Work with what you have and save for a machine that has all you want.