Brush away any debris that has built up around the drain cap, by hand. Cleaning the surface of the yard drain frequently will prevent deeper clogs later.
Remove the cap by lifting it off the drain and inspect the opening for any clogs. Pull out any debris from within the drain by hand and discard.
Place a hose down into the drain, about a foot from the opening, if a clog further within the drain. Turn the water on full blast to dislodge any possible debris found beyond an arm’s reach.
Thread an auger, or plumbing snake, deep into the pipe if the hose was unable to dislodge any debris. Rotate the handle on the auger to swing the steel tip around inside the drain to clean.