Landlord Demanding Notice After the Fact

This regards landlord/tenanat law in Washington state. I'm renting a furnished rental, month-to-month. The landlord was verbally informed I could not give extended move-out notice due to the nature of my job; I assume that's why he crossed out the paragraph on "Lesee's Hold Over" which states:
"If leesee remains after natural expiration of agreement, a new tenancy from month-to-month shall be created which shall be subject to all terms and conditions hereof except that rent shall then be due and owing at ___DOLLARS___ per month and except that such tenancy shall be terminable upon 30 days written notice served by either party."

Other than that crossed-out paragraph, nothing in the leese requires giving notice to vacate. I've since informed the landlord I'm moving out in 12 days. His first response was to complain he didn't get 30 days notice. He later researched WA state law and discovered a landlord can only demand 20 days. Now he wants to charge me another month for not giving 20 days notice - even though he crossed out the only thing related to that in the leese. Am I liable for an extra month because this landlord forgot to stipulate his notice requirement in his leese?

What constitutes one rental month in Washington state? Is it 30 days, or, for example, Feb 5 to March 5? Also, when does a "term" begin if not specifically noted in the leese (mine simply says "month-to-month"?). Is it the day one moves in or the day the leese is signed?

Thanks in advance for your help,
Oliver

The most common type of tenancy is a periodic tenancy, for example, a week-to-week or month-to-month tenancy. A periodic tenancy is automatically renewed unless either the landlord or the tenant gives written notice to terminate the tenancy at least 20 days prior to the end of the month. The tenancy cannot be terminated in the middle of any month unless the landlord agrees. Similarly, the landlord cannot terminate the tenancy except at the end of the month and only after twenty 20 days' prior written notice to the tenant.

I got the above info off this site: http://www.wsba.org/media/publicatio...ord-tenant.htm

Looks like you have to terminate at the end of the month. Meaning that you can give notice anytime as long as it is 20 days before the last day of the month. Example: February has 28 days. You cannot terminate the tenancy except at the end of the month so the 28 is your last day. You will have had to have given notice that you are moving out on the 28th by Feb. 8 (Feb. 7 just to be sure).