with 400 of those I pray to our maker that they are kept in a tightly sealed steel container. Spontaneous combustion is spooky. We have these almost 4 foot long thermal probes for compost heaps and the surface can be with frost and ice on it. and 4' in it can be 200 degrees and almost ready to ignite.
As for cleaning them, throw some TSP in with the simple green. If you want to clean the inside of the washer out when you are done, WD40 on a paper towell works really well. We've found lately it is cheaper to just toss them once they get too dirty but we do it on trash day so they don't sit out in the trash for a week and combust.
Here is how to from online on how to get them to ignite in under 2 hours:
Instructions.Things You'll Need:
Two or three pieces of dry cotton rag, one foot squares
Bottle of linseed oil
Small metal can (an empty small coffee can)
Bathtub, large sink, or any place void of flammable materials with easy access to water
Rubber gloves
1.1
Soak the rags. Make sure when you start with your rags, they are not damp at all. Wearing rubber gloves, douse the rags thoroughly with the linseed oil until they are dripping.
2.2
Place the rags in the can. Make sure to stuff the rags into the can so there is as little room as possible. The more crowded the rags are, the quicker the fire will start.
3.3
Wait for the rags to heat up and combust. Place your can of oil soaked rags in a safe place, like a tub or large sink with no flammable items nearby. Make sure water is readily available. Linseed oil evaporates very, very quickly. So quickly, in fact, that the linseed oil's act of evaporation heats up whatever material it is evaporating from, like a cotton rag. If there isn't enough air around the rag to enable it to cool itself while the linseed oil evaporates, the heat from the evaporation will rise to the point of combustion. Give your can of linseed rags a good forty-five minutes to two hours. After this time, the rags will probably at least have started smoking, if not burning outright.
Read more: How to Start a Fire With Rags and Linseed Oil | eHow.com
http://www.ehow.com/how_4478470_start-fire-rags-linseed-oil.html#ixzz1GGIa0oof