How to completley flush cache?

I need to flush cache so a Duplicator Pro package build can complete. I’ve gone to the W3TotalCache dashboard and clicked the button to clear all the cache. I get a message that it is cleared but when I go back to build a package in Duplicator Pro, it won’t complete because there is too much cache. Duplicator Pro says there is 19.93MB in the ‘/wp-content/cache’. The cache size minimum threshold is set at 1MB.

I looked at the FAQ for
“How can I flush the cache without using the WP Admin interface?” But I don’t know where the following code should go:

"It's possible to empty the entire cache or simply purge the cache of a single post / page:"

Purge the entire cache of html content:
if (function_exists('w3tc_flush_posts')) {
w3tc_flush_posts();
}
Purge a single post / page by passing it's ID:
if (function_exists('w3tc_flush_post')) {
w3tc_flush_post($post_id);
}