On pulling a sample, short of installing a sample cock in an external oil line, I would drive the truck until everything is up to normal operating temps. wipe the area around the oil drain plug clean, remove drain plug and let about a gallon or so of oil go. Then catch your sample. It is easy for me because I have the large mouth sample bottles. It is very important that if you are going to use a catch bottle that it is absolutely clean so as not to contaminate your sample.