There ARE toilets at Stratford Domestic. I can't remember the platform number, but they're on the Southbound Platform Side of the
DLR▸ (Towards West Ham). However when I was there on Friday, they were closed due to vandalism (Not surprising for the area).
The are plenty of toilets however in Westfields which is practically right on the main entrance. There are several toilet rooms there, one of which is a very short walk into the shopping centre and is clearly signposted. I reckon even for a slow walker, it would take 3 minutes to get to the karzi's. All the loo's in Westfields are free, very clean and staffed by attendants. I would say it's worth the walk over using the Stratford Station Bogs. Even the Disabled one is closed!
Also the Barrier Staff at Stratford would have to let you out if you wanted to use the toilet because the loo's at the station are
OOU▸ ! A similar situation applies at West Ham, A Station with 8 Platforms and NO toilets! However if you ask the barrier staff, they will let you out and there is an automatic 20p per use toilet just outside the station to the right. It's not an overly pleasant bog though.............
Avoid Starbucks which is just inside the Westfields/Stratford Station Entrance if you intend to "buy-a-coffee-and-pee" as they quite often refuse to open the only toilet in there for you unless you have a small child