The symbolism seems to be a very strong parallel, because at that point L was trying to test the 13 day rule based on his suspicions of Light, so the idea of washing the feet of the betrayer/sinner fits nicely, way better than the awkward gay implication (getting sexually involved with someone who you're trying to convict and put to death doesn't add up in my opinion).
I do not think Light could possibly be gay for L (Light said he would give L friendship if that was what L wanted, but Light always wanted L dead). Just as Light is a dominating manipulating person, using everyone around him to achieve his goal of become the God of the New World, I also think this Light would be the dominating person in regards to his sexual activity (not shown in the series). After L was eliminated and no one really suspected Light or Misa and Light and Misa start living together and Misa was always wearing revealing clothing whenever at home, I am almost 100% confident that Light was using Misa sexually on top of using Misa to advance his agenda. Also, there is the implication of Light's sexual involvement with those girls who he could call up for a date in High School (remember his "popularity status" from the episode with the Space Land bus jacking). Basically, Light is a player, a straight player at that, in my opinion.
As for L, I must note that L seems to have a higher discipline as the loner and anonymous L, capable of rational thought even in the most stressful of situations. It wouldn't be too hard to speculate that L was not as affected by sexual desires as other individuals. On another note, L was from the Wammy House in Britain, so L would have definitely been exposed to western ideologies, including Christianity.
However, I suppose everyone can have their own interpretation. There really weren't any sexual scenes defining that aspect of their lives so you can fill in the blanks with whatever you want.
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