I am an amateur grower in Northern California, and have had problems with rodents chewing through my drip tape (even when buried). Because I’m not there every day to check for leaks and make repairs, I needed an extreme measure to protect the line from rodents. The solution shared here is “armored drip tape,” or running the tape through a flexible metal conduit commonly used to protect electrical wiring. After this, there was no evidence of rodent damage, even when the drip tape was full of water under drought conditions. This solution can be expensive, but in my case it was worth it to avoid having to repair the drip tape all the time.
Flexible metal conduit consists of a spiral (helix) of metal with a seam along the spiral where water can leak through. With my low-flow drip tape setup, Irritec P1 Ultra 5/8" drip tape - Wall Thickness : 15 mil - Emitter Spacing : 24" - Emitter Flow : 0.33 GPH , and fairly low pressure (at most 8 PSI), water leaks out of the conduit, localized around each emitter.
DISCLAIMER 1: I have not tested higher flow rate emitters. At higher flow rates, it is possible that water could pool in the conduit rather than leaking through locally at the emitters.
DISCLAIMER 2: I have not tested the water coming out of new or corroded conduit for safety to crops or humans. Because galvanized and stainless steel are used in irrigation systems, I would hope that water in contact with galvanized or stainless steel conduit would not produce harmful products, but can make no guarantee.
DISCLAIMER 3: The conduit will corrode eventually, and I have not tested it over rainy seasons and long time scales yet, but I believe it is ultimately worthwhile compared to constant leak checks and repairs without it.
Step by Step Guide:
1. Obtain Conduit
Use flexible steel conduit, either galvanized or stainless. For 5/8" drip tape, 1” conduit would be ideal for easily pulling the tape through. However, 1” conduit is more costly and harder to come by than 3/4”. So I chose to use ¾” and deal with the added challenge of pulling the tape through. Avoid “liquid tight” conduit (this is coated with plastic and does not allow water to pass through). Avoid conduit sold with industrial lubricant already applied to the inside. Avoid Aluminum conduit.
2. Obtain Fish Tape
Drip tape can be pulled through the conduit using a tool called “fish tape” that is traditionally used to pull wire through conduit.
3. Prepare The Conduit
For each drip tape run, determine how much length you need and cut the conduit (you can use metal shears, and it helps to punch a hole in it first). Because of the tight fit of the tape in ¾ conduit, it gets hard to pull the longer the length. The longest single section I pulled was 100 ft. You can pull through one section at a time and then join the sections together for longer runs.
4. Uncoil the fish tape out to the length you need to pull, and run it through the conduit until the “hook” end comes out the other side (I would not recommend uncoiling the fish tape directly into the conduit as this can bend it).
5. Hook the Drip Tape on to the Fish Tape
Take the end of the drip tape you want to pull in to the conduit, and punch a hole through the middle about 4 inches from the end. Make the hole just large enough to pass the fish tape hook through. Finally, take the 4 inches of drip tape extending past the hole, bend it in half, and tuck it in to the hook.
6. Pull the Drip Tape Through the Conduit
If you chose to use 1” diameter conduit, the drip tape may pull through easily and this next step may not be necessary:
3/4" conduit has an inner diameter of 0.81 inches, too small to pull through flat (un-inflated) 5/8" drip tape. However, you can pull it through by shaping the drip tape into a cylinder as you pull it (similar to the shape it would take on when filled with water). This is a two person job where one person at the “exit” of the conduit grips the conduit and pulls on the fish tape while another person at the “entrance” of the conduit feeds in the drip tape while shaping it. Drip tape can be shaped into a circle by pressing inwards at the edges of the tape. (It seems to be the area around emitters that gets stuck and needs shaping the most, but I found it easiest to shape the whole length of it as it was pulled through). It helps apply a lubricant to the drip tape as you feed it in, such as a mix of bio-degradable soap and water.
7. Protect End Caps and Joints in the Drip Tape
You can either wrap hardware cloth around them, or, for extra protection and ease of access, put them inside electrical junction boxes designed to mate with the flexible conduit, and run the drip-tape-in-conduit into those boxes. Where the drip tape taps off of the main line, I wrapped hardware cloth around the joint and the conduit leading in to it.
Side Note: Rodents have not chewed through my unprotected 3/4“ PE main line so far. Maybe it's too wide for them to get their mouths around, or too out in the open for them.