Some Lutheran churches have an extra drain in the kitchen (sacristy) sink. This extra drain dumps directly to the soil underneath. The idea is that it is more respectful to dump on soil than to mix with sewage.

Some Lutheran churches have an extra drain in the kitchen (sacristy) sink for disposal of extra, unused communion wine. This extra drain dumps directly to the soil underneath. The idea is that it is more respectful to dump on soil than to mix with sewage.

Page 13 of this FAQ from the LC-MS Lutherans explains their policy on disposal of the communion elements, including "returning to earth".