I recently took a long distance train trip (3 days) in a bedroom unit. However, I don't think I ever used the shower in the room--it is extremely small and I can't imagine the water pressure being great. Instead, I used the "communal" showers downstairs as suggested by people on the Amtrak forum. These showers are reserved for people in either roomettes or bedrooms, so not really for the whole train. I think very few people used them since they looked dry whenever I used them. They were regular sized and had great water pressure. However, it was quite hard to control the temperature. Once the water got hot, it stayed scalding hot and no way to turn the temperature down! I figured this as a way for Amtrak to save water (and it worked, because I turned off the water whenever I soaping up instead of keeping it on all the time as I normally would). Anyway, I was able to wash my (long) hair easily in the shower. I usually never use a hairdryer, but there are plugs in the bedroom by the bathroom.

Also, Amtrak only provides (cheap) soap in the bedrooms/showers so I would definitely bring your own toiletries.

I used facial wipes (made by Ponds but I'm sure there are other brands available too) to clean my face in the morning. The sinks water supply are really not great for washing (you have to keep pressing down on the lever, and the water coming out is very "splashy"). The wipes were great (I use them when I travel on planes as well). I also used body wipes as a quick refresher (especially since the shower isn't that convenient to use). You don't move around too much during the day and the train is air-conditioned so the wipes work okay.