Penrose drains are thin-walled latex tubes that do not actually carry fluid, but simply maintain an open portal from the wound bed to the outside that allows wound fluids to exit. Vets place Penrose Drains in the wound bed surgically, at the time of wound repair. These drains are also commonly used to keep draining abscesses open.
Only remove these drains when instructed to do so by your vet. In many cases, vets will want to remove the drain themselves so that they can assess the wound at the same time. Penrose drains are usually secured by a skin suture at the top part of the drain and another at the exit point through the skin.
Halter your horse. Gently dab both sutures clean with a dilute antiseptic like 1:10 betadine or 1:10 chlorhexidine solution. Dab until the paper towel is clean.
Start with the top suture. Grasp the suture end with forceps. Gently pull the suture away from the skin, raising the knot slightly above the skin. You should now see both sides of the loop going into the skin. Cut only one side of the loop under the knot. The loop should now pull out through the skin, freeing the drain. Repeat on the other knot. Now grasp the drain with forceps or fingers. It should slide out with no resistance.
Tips for safety & Success
Be sure your horse is adequately restrained for this procedure. An assistant holding the horse's head is helpful.
In the case that both sutures have been cut, and the drain is still anchored, do not force it. It is possible that the drain has been caught inadvertently in the suture line. Talk to your vet about the best course of action.