I’m sorry it took me so long to respond. This question actually got me spinning for a while. I wasn’t sure how to respond and I wrote a few different responses, all of which I have abandoned. Here’s my short answer:
Your query seems incomplete. You understate your interest in butt play as “slightly intrigued,” which I assume means you are slightly intrigued.
“Butt play” can mean so very, very many different things to different people. It’s really general.
In the context of jacking off with a buddy, I love light butt play myself. It’s not allowed in pretty much any JO club, but privately, it gets me off big time.
While you’re enjoying one of your “very satisfying mutual hand jobs,” just play with his nuts while you or he strokes his cock, and move back gradually under his scrotum to the area of the perineum between his balls and his butthole, and just brush your fingers over the buthole. Try just gently stroking the whole area of the perineum without pushing a finger inside and see how he likes it.
You can ask him to reciprocate or see if he does so without asking.
That’s literally playing with the butt. If what you’re talking about involves fingering his or your own hole and exploring prostate massage, start by getting to know your own hot buttons during solo play. You can use your finger or try a toy. There are lots to choose from.
I also heartily recommend a little self-education from this most excellent book written by really smart, sex-positive people.
Bottom line (all puns intended), bring it up to your buddy and talk about it. Find out what he’s interested in if anything more. Moving along this path has to be consensual. Jacking off requires very little prep or experience. All guys know how to do it, even though some basic protocol is worth setting to make the sessions satisfying. Butt play is different because of the very present risks of A) transmitting diseases and B) poo.
So my advice is to play with your own butt and become an expert at stimulating your own prostate, educate yourself on how to prepare for and share the pleasure and most of all, don’t be afraid to talk about it.