Since this site doesn't get alot of responses, I would try the site below. Ally http://www.irrigationtutorials.com/dripguide.htm

Take a infilter out of it's casing, roll up some shade cloth in a 30 mm long cylinder the diameter of the casing and put in one end. In the other end you put in your fertiliser and screw the end on. If the fert is to strong put a T piece in before and after the casing. Join some hose to the T pieces with a tape in the middle to regulate the water to dilute the fert to the required strength.

A tip on installing the drip units. Don't try to twist them into the end opening of the 1/4 inch hose. Insert the end of the drip unit into the open end of the hose then do a side to side bend while applying forward pressure on the hose and drip unit. Continue until the end of the hose is up against the flared section of the drip unit. To remove a unit just use your rose clipper and cut the hose off in slices until it comes loose. Have fun.... Oh, don't forget to install 'back flow' unit AFTER the on/off switch. AND it must be the highest point in the drip system. Rule of thumb, one 1/4 inch hose with drip units can service up to 60 plants at 1 gallon per hour rate. While you're at the store pick up some 'goof plugs' you'll need them sooner or later!!

Thanks for the response and suggestions! Meantime, I found some check valves that can be put in-line with standard pvc pipes, the skinnier ones that get buried underground. I might try those, not sure if I would put them up top at the patio or down below. Apparently there should be a backflow somewhere, however, I could not find it. Here are some photos, not sure if they will be helpful. Property shutoff. The bell thing looks like a vacuum breaker or backflow preventer. This shuts off water to the house and irrigation. There's another valve at the street in front of the house. Here's the irrigation shutoff Here are the three valves. One is separate from the other two. They appear to be rainbird asvf series. These should have anti-siphon built in. I do not see any pressure regulators. The emitters do seem to be running correctly, so perhaps the pressure regulators are buried underground? Thanks again!