Do I pay tax on the wash sale gain? For example, sale 10 shares of X at a gain of $1000 and buy back 10 shares of X stock on the same day to qualify for a wash sale.

What you just described is not a Wash Sale.  Since you sold the first 10 shares of X at a profit, the subsequent purchase is not a wash.  You do owe tax on that $1,000 gain.  A wash sale will be clearly indicated on your 1099-B.

A wash sale occurs when you sell a stock at a loss and purchase the same stock 30 days before or 30 days after the loss.

In that case the loss is added to the basis of the repurchased shares.

See Wash Sale Rules Section 1091(a) on page 6 IRS.  Application of Wash Sale Rules to Money Market Fund Shares 

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