I appreciate that incontinence - urinary and bowel incontinence - is not exactly great dinner table conversation. When talking about such issues in the context of specific labels, there's also the possibility that stigma can result, which in turn can affect the outward view of that label. But incontinence can be a life-changing prospect for many people (and labels); realising the scale of the issue is the first step towards providing appropriate screening and also management onward to improving quality of life...
With such an issue in mind, I'm introducing the paper published by Justine Niemczyk and colleagues  who took a look at the collected peer-reviewed research literature covering "the co-occurrence of nocturnal enuresis (NE), daytime urinary incontinence (DUI), and fecal incontinence (FI) in ASD [autism spectrum disorder], and vice versa, of ASD in children with incontinence." I might add that this research group are no strangers to this topic (see here).
After picking out over 30 publications, authors managed to 'boil down' the literature to a few principal statements, most importantly including "The published literature implies a higher prevalence of incontinence in children with ASD compared to typically developing children." They also noted that: "ASD symptoms are found in incontinent children" but caution that "no study included a non-ASD control sample."
Acceptance that autism and the bowel for example, represent an important pairing for quite a few people (see here and see here) is growing as the years pass by. It's no longer a 'taboo' point to say that both functional and potentially more pathological bowel symptoms/conditions are over-represented in relation to a diagnosis of autism and appropriate screening and management should be in place save any further health inequalities appearing. Clinical practice however, still has some 'catching up' to do when it comes to those points about screening and treating such issues; specifically, not just assuming that 'it's all down to their autism' or providing some fluffy psychological explanation when it comes to the appearance of such issues. A diagnosis of autism is seemingly protective of nothing (see here for an example) and the onus is to screen and rule out first before making any grand judgements...
Alongside there is also quite a bit more to do in this whole area as Niemczyk and colleagues note, both to improve the quantity and quality of investigations in relation to incontinence and autism. In the meantime, there is guidance out there for potentially dealing with such incontinence issues as and when they arise (see here) with the added proviso that seeking professional help is a must in this area bearing in mind the variety of 'causes' potentially behind such issues  which might need to be examined.
 Niemczyk J. et al. Incontinence in autism spectrum disorder: a systematic review. Eur Child Adolesc Psychiatry. 2017 Oct 10.
 Afzal N. et al. Constipation with acquired megarectum in children with autism. Pediatrics. 2003 Oct;112(4):939-42.