How do you focus the energy and buildup

The first part of what you describe sounds similar to what I feel with my prostate orgasms (but not with other orgasms, nipples, testicles, etc).  That is, a build up of electrical current, that tingles or heats up my body.  Sometimes I chase them, sometimes I surf on the edge to see if it will get bigger that way, sometimes I avoid them and let them overtake me like a tsunami. I rarely don’t clench, as non-clenching results in little sensation. The peaks for me are occasionally calm seas, but more often than not they are more seizure like—tension all over, shaking, uneven breathing, screaming… 

I haven't ever been able to experience a super O without something inserted in my anal canal. Ove the years I have become so re-wired that it's hard for me to have an orgasm through PIV sex or through manual stimulation of the penis only. I have to have something in me - MGX, Peridise, butt plugs - something. I no longer get any sexual satisfaction from my penis alone. My main erogenous zone is my ass and I have something up there to get off.

I insert a well lubed toy.  It starts out with a few minutes of feeling nothing other than a full feeling up my ass.  After a while, my body automatically starts a slow, light, involuntary clinching of the sphincter. The pleasant feeling in my ass gradually starts to build, and my focus becomes centered on what's going on in my anal canal. The clinching becomes stronger and more frequent.  Then it feels like there is this intense itch throughout my entire rectum that needs to be scratched and the clinching becomes more and more intense and uncontrollable as the tool in my ass searches for that itch to scratch. I start an uncontrollable shaking and clinching, and my breathing becomes rapid. Sometimes I start to moan. The intensity of the sensations continues to build on each other to the point where I have to stop to catch my breath.  I lay there until things calm down and then the cycle starts all over again and again.  Sometimes this goes on for up to two hours.

When I'm finally worn out, I remove the toy from my ass and lay there trying to recover.  I still have a slight buzz in my ass, but there is no longer that buildup of sensations once the toy is removed from my ass. It is more of a tapering down to a normal. The entire process is so pleasurable that it has become addictive for me.

I focus on control. I guess I always have done. As energy/pleasure builds,I direct it to the anchored tension I hold in the pf. I’ll contract to push the energy higher,then ease of and tether it to my AT so it remains at that level. Then contractions again to rise it further,then tether again. This way I can set the tempo for what we’re in the mood for and only need some very light contractions that will cause wave and peak mo’s. I like to float on calm seas,but sometimes I just need it to be hard. 

@studmouse47, what you described is remarkably similar to my progression. I have lately been able to continue without a device inserted, especially if I have just pulled the Tempo out.