@7deepIrish, I think I know your problem. If you can't do as big an enema on the second time, then unless you are using very hot water or harsh solution that makes you close up, your problem has to be that you are not doing a complete expulsion of the first enema.
I do bathtub expulsions, (with a bleach and deodorant cleaning afterward.) To get a good expulsion, I do 2 rotations between being on my back, on my left side, and I standing. This helps it all come I also massage my stomach along the path of my colon (from right to left in a big inverted U shape) to squeeze and push it all out. I also I also use a 10-lb weight to help me squeeze and push. Sometimes it takes 10 or 15 minutes to do a near complete expulsion, and sometimes a lot less time.
To do a deep cleaning for a clean playtime, you need a series of high-volume enemas, (multiple quarts.) Have you tried a retention butt plug nozzle to go higher volume? I use the Silicone Nozzles SPD3.0 retention plug in EXTRA SOFT silicone. It completely seals my colon. If your colon can hold a gallon, this retention plug will make sure it goes in. You might have work through cramps and strong urge to expel on your first big filling, but the retention plug makes it much, much easier to hold it all in. After my first gallon and a near complete expulsion, the second, and following gallons go in effortlessly and pleasurably.
My deep cleaning routine is 5 gallon-bag enemas with good expulsions in between. The final expulsion.needs to be complete as you can make it. The process takes 60 to 90 minutes, but its worth it if you do it right.
Yesterday, I did a deep clean out. I didn't have to go to the toilet at all afterward and I didn't leak. I got out our monster 24" 2.75-inch diameter double dong, and I dropped it in my wife's lab. With a big smile, I asked, "Would you please fuck me with this?" She did, 12 inches in and out for 15 minutes. After I shot my load, she pulled the monster dildo out of me, and it was perfectly clean. I did dribble maybe a tablespoon of lube and mucus on the towel, but that was it. It was very clean considering what we did.