Toilet breaks are the monkey I've been carrying on my back since April 2022 mate.
Manchester marathon cruising along, 5 miles to go until I finally get sub 3, stopped for a piss, couldn't get back going again, hobbled in at 3hours and 14 seconds.
It's tricky mate, have to experiment a lot with what suits, which gels won't go straight through you, I never really take much more than a sip of the water they give you on the way round, I think it does go off a bit the more used your body gets to the high miles as I'm not as bad as when I first started.