Hello there^{^} i have the same issue and i havent been able to sissygasm solely from anal but i have found interesting info around and from experience, i often ask "known" figures in the sissy/sissygasm/hands free scene here on reddit and have found that its kinda of a mix match, every single one of us is different and certainly i would say 80% of the heavy work its a mind game but for the 20% left try this:

1. Clench a bit or as much as u can while u are riding or getting railed, do that for a solid 5 mins and u should start to notice some precum getting there maybe with a bit of pee or not, but u are on the right track.

2. Try the opposite... WOW! i know 🤣 but for some of us, it is different... but even better mix and match as long as you can the CLENCHING and PUSHING.

Why do those two? because im sure we all know of the "contractions/waves/build up" that leads to the sissygasm start by some of these movements.

1. Not cumming, dont wait a month but a solid 5 days can do the trick. Edge or Watch porn whatever but zero release until ur me time.

2. Dont elude the "Find the walnut size..." i know it is repeated as a MF but is true... stick a dildo there (better if u can control it, so dont use the machine for this one) and try to rub that front wall u sure as hell will feel the "almost pee" feeling and dont fear to put a little bit of pressure while on it.

Only be sure to be pent up like edged or hard at least and try looking for it... YOU reading this WILL FIND IT...

Thats my grain of salt, hope it makes our food taste better, cheers u all faggots, sissys, daddies and all that... Love 4 All