Going to need a bigger bowl

I've been battling this potty training thing for sometime - not for myself - my child, and I'll even throw the other one in there too for shits and giggles.  I am so bad at potty training that my oldest has something called "encroporesis," which essentially means he holds it so long that he will shit himself uncontrollably causing his colon and rectal muscles to lose function.  I can not make this up.  Pooping has been such a traumatic thing that he would rather not do it.  If you can't poop on your own toilet, where can you poop?  Apparently in your underwear if you ask him.  So now that I've overshared you know my backstory.

Here's the revelation I have stumbled upon...my toilet is not big enough!  No Dr. Sears book or self-help internet website necessary.  Cameron goes in the tub at bathtime, we dump in every toy we have, we throw in brother, and BAM!!  That digestive track kicks into gear and his colon sighs in relief.  Instant panic sets in.  What child do I save first from the floating logs of contamination?  The bath water starts swirling in a sea of brown and decisions have to be made.  For some reason impulse causes me to get the culprit out first and heave him on the potty.  He always looks at me in disbelief like, "Did you not see the poop in the tub?  I'm good."  I reach to save the little one and before I can throw him a life ring, I see his hands are now squeezing his new bath toy.  Prayers are sent up, "Please dear God just don't let my child eat the poop."  My parenting skills have been exhausted at this point, and I keep the little one in the tub dangled under running water.  Where are the instructions on this?  "Mama, can you clean my booty?" is replaying about 100 times a minute while I try to explain to a three year old that a dirty booty is not top priority right now as I have a two year old who may or may not have INGESTED the shit.  

I feel like I have typed a post like this before.  This happened a couple of times and the reign of terror is happening in full force as little brother is now taking cues from the big one.  Just as soon as the water has reached optimal temperature and every toy has assumed its rightful place in the jacuzzi of filth, my kids unleash all they have to offer and it's every parent, child and toy for himself.  
 
I can't decide if I just need to take the toilet seat off or if I have to fully submerge booties in order to get them to poop in the toilet.  Either way this does not give me good feelings about putting them in swimming lessons.