Deuteronomy 23:11

9When you go out and camp against your enemies, then you shall keep yourselves from every evil thing.

10If there is among you any man who is not clean by reason of that which happens to him by night, then shall he go outside of the camp. He shall not come within the camp;

11but it shall be, when evening comes, he shall bathe himself in water. When the sun is down, he shall come within the camp.

12You shall have a place also outside of the camp where you go relieve yourself.

13You shall have a trowel among your weapons. It shall be, when you relieve yourself, you shall dig with it, and shall turn back and cover your excrement;