You must know what breast pumps are!
The ones I use are designed to express the breast milk from lactating women, but as a transfemale who craves large wobbly breasts, I use them to suck me out, increase my nipple & breast volume and hopefully, someday, to induce milk flow.
Apart from that, the sheer sensation of being sucked hard is wonderful especially when fully dressed in bra, heels, makeup etc.
I am being sucked hard as I post. I use an Ardo Calpso dual electric pump on the maximum setting. I lubricate myself with Johnson's Baby Oil before commencing.
My nipples are currently 2" into the breast pump funnels. I have been pumping for nearly an hour and I am really aching, but I will give it another hour.
After releasing from the pumps, I have really proud nipples, and to prevent my bra from inverting them, I slip on a pair of nipple shields.
It's working:I have gone up a cup size and I can't go without a bra anymore. Going upstairs braless is a bit painful.