This is a copy of a comment left on my blog
http://eghea.notlong.com
Hi
I followed and enjoyed your garden blog through the summer of 2007. Found your 2008 blog today. I am from India, where a kitchen is incomplete without a pressure cooker. We cook every thing in it. From rice and lentils to meats. You can use the pressure cooker to steam foods, if you take off the 'rocking exhaust' as you call it. We just call it the whistle. Because that's what it does. Also, if you want to heat something, put the lid on with the ring, but don't put the exhaust on. This method will work for both steaming things in your colander as well as heating.
I am surprised that vessels weren't included in your purchase. In India, when you buy a pressure cooker, it comes with three interlocking cylindrical steel vessels that fit into the cooker. As well as a perforated base, which is put on the bottom of the cooker to prevent the clogging you mentioned. Maybe I will post pictures of the assembled cooker on my blog and send you a link. I am sure you will be able to find similar pots around the house.
Also, I am sure you do this, but make sure to take off the exhaust before each time you cook and make sure the path for the steam is clear through.
To increase the life of the ring, you may want to remove it from the cooker, wet it and stretch it lightly before you operate the cooker.
Happy pressure cooking !