Lymph is fascinating. It is your other circulatory system.

Capillaries are are so narrow they can only allow a single erythrocyte through at the same time. The pressure from your heart causes fluid leakage from the thin vessels. Lymph ducts/nodes help get this fluid back into your blood. Since the heart doesn't pump lymph, that helps move it through your body is actually your musculoskeletal system. That is to a certain degree true from your venous / return flow in your "normal" circulatory system, too. It's why your feet can swell if you're sitting down too much. I'd speculate that lymphatic flow efficiency has local and systemic elements that contribute to it (and so your leg muscles moving lymph help your overall lymphatic system health).