One issue we really struggle with concerning our most severe SPD child is handwashing. Now, I'm not a germaphobic in any way. I think that things like hand sanitizer has it's place but I also think that people can over do it. However, handwashing is important and when your child struggles with control issues like mine does it becomes more of a hygenie problem.
One of the things I haven't done but should is find a handwashing poster for each bathroom for him to learn how to follow the proper steps of handwashing. My son knows the steps but it's kind of like I have to be a bathroom monitor to make sure it happens. With my middle child I can't keep her out of the water... or soap.
Another issue is that wet sleeves tends to be an issue in our household. I think this is one huge reason why my kids tend to wear short sleeves or not wash their hands. My middle child has gotten used to dealing with this due to being in preschool. Helping a child role up their sleeves and immediately pull them down can be helpful after handwashing.
Another thing that works for us in a pinch is babywipes. For my son this is not something we strongly encourage but it works in those rush where I can't get him to wash his hands. It's a compromise that we sometimes make due to melt down issues. It's not often but we do use this method sometimes.
Hand sanitizer is other option in some places. The problem I have found with this is some of my children tend to lick the liquid gel of their hands. YUCK! Due to an allergy to various chemicals that are in soaps and household products I have to be very careful even with hand sanitizer and so this is not a good option for our family. Rather than deal with the gel I'm almost always guarenteed to have to deal with and touch I have found that the foam type works better for us.
Other ideas that I haven't tried but you might consider is using a wet washcloth to wash hands. If your washclothes are rough you can buy the baby washcloths which are a lot softer than regular ones and they don't have the bumpy texture. Using the spray feature that is on a lot of kitchen sinks or the shower if you can take the handle off sometimes works especially if they have different speeds.
There is one more product that I am going to list later on for this issue simply because I do have some of the products and LOVE them. It is a body washcloth that you don't need to use soap with from Norwex I believe. I'll see if I can find the website of the sales person I go through in case you are interested in purchasing something like this. It works well for people with sensitive skin.