In SKIMT's post I mentioned a modification to his dry bag that would help with doing laundry on a trip. Here is what I have done to an Outdoor Research dry bag to give the inside a washboard texture so you don't have to put in as much effort to get your clothes clean.
Step 1.) Obtain supplies, for this I used a 15 litre Outdoor Research graphic rolltop dry bag although any polyurethane coated nylon dry bag will work, Seam Grip and a hotel key card*
Step 2.) Notch key card, using a sharp pocket knife CAREFULLY cut little V-shaped notches on one edge of the keycard.
(If you are in DeKalb, IL you can use this opportunity to order pizza!)
Step 3.) Turn bag inside out and glob on the Seam Grip, lay the bag flat, you will probably need about an ounce or so per side.
Step 4.) Spread out the Seam Grip, don't worry about getting it perfect.
Step 5.) Wait, Seam grip wants to settle thin and flat, great for tent seams, not so good for this project.
Step 6.) Once the Seam Grip has cured enough to become thicker and is holding it's shape use the notched key card like a tile trowel to make ridges in the seam grip, press pretty hard to get right down to the nylon in the grooves. Move in whatever pattern you think will work best for cleaning your clothes, I chose "gentle wave".
Step 7.) let cure, but watch it, if you didn't wait long enough it will try to pool so it is flat again, expect some rounding of the ridges but if it starts to really flatten give it another go with the key card.
Step 8.) Once it has become semi-hard let cure overnight. (Optional but not necessary: do same to reverse side)
Step 9.) (next day) turn right side out, fill with dirty clothes, soap and water. Let out excess air, seal roll top and roll around to scrub away! Rinse, repeat as necessary.
* I always keep my hotel keycards, not for security/privacy reasons but for the fact that when I am on the road the tour manager is usually the one that has booked the hotel rooms and even the simple act of handing back a room key to the front desk will trigger a series of events that has the front desk clerk interrogating me about credit cards and room service charges for a dozen different rooms and trying to get me to sign off on everything and making me late for bus call, so sometimes it is better to sneak out the back and hold on to them to use for little DIY projects and leave the tour manager to do their duty sorting out rooms.